1. Field of the Invention
The present invention relates to a sheet through type image reading apparatus which reads an image on a document while being transported by an image reading portion which cannot be moved.
2. Related Art
In a sheet through type image reading apparatus, an exchangeable image reading portion and a document transportation path which is curved so as to move around the image reading portion when viewed from the side are included in a housing. As an image reading portion employed in an image reading apparatus of this type, a Contact Image Sensor (CIS) which is light weight and small in size is used in many cases so as to be arranged in a narrow space. The CIS has a narrow focal depth when an image is read. Therefore, an image reading roller is provided so as to be opposed to a reading position of the CIS and a space between the CIS and the reading roller is kept to be narrow so that an image on a document which passes through the space is read. When an image is read, the reading position of the CIS and a document is slid contact with each other so as to easily generate static electricity. In particular, static electricity is significantly generated under an environment of low humidity. Such static electricity may cause malfunction or failure of the CIS. Therefore, exchange frequency of the CIS is high among electrical parts constituting the image reading apparatus.
In terms of this point, a following configuration has been disclosed in Japanese Unexamined Patent Publication No. 2004-336270. That is, a reading roller which is arranged so as to be opposed to a reading position of a CIS is detachably inserted to an opening. The opening is provided at a lower surface side of a housing. Further, the CIS is detached from the opening from which the reading roller has been detached in a downward direction. With such configuration, there is an advantage that workability when a service person detaches the CIS in a market can be improved.
However, in the above-described conventional configuration, the following problem is caused. That is, the reading roller which is arranged so as to be opposed to the reading position of the CIS can be detachably inserted in the above-described conventional configuration. Therefore, every time after the CIS is exchanged, the CIS is required to be attached while positioning the CIS and the reading roller at high accuracy and adjusting a space between the CIS and the reading roller and attachment postures thereof. Accordingly, even if the CIS is easily detached, time and effort for attaching the CIS are required (workability for attachment is bad).
Further, when a sufficient attachment accuracy is not ensured because attachment positions of the CIS and the reading roller are deviated, there collaterally arises a problem that an image reading accuracy by the CIS is deteriorated, or skew of a document or a paper jam is caused. That is to say, when the CIS is exchanged, it is preferable that mechanisms represented by the reading roller, which deeply relate to a document transportation accuracy or an image reading accuracy, be not attached and detached if possible. As the mechanisms which deeply relate to a document transportation accuracy or an image reading accuracy, rollers, guiding members, and the like which are arranged at a transportation downstream side with respect to a skew correction roller which corrects skew of a document are exemplified.